So now we know how Supreme Court justices are appointed—but appointed to do what, exactly? We know that the US Supreme Court is the highest tribunal in the nation, but as the leader of the pack, what sorts of cases does it hear and how do its rulings affect federal, state, and local law? Perhaps the easiest way to think about the answers to these questions is by considering the scope of the Court's jurisdiction—its authority to hear particular cases.

First, in certain circumstances, the Supreme Court possesses original jurisdiction—that is, the power to review a case before any other court. Article III, Section 2 of the Constitution gives the Court primary and exclusive authority over all disputes involving two or more states and all cases against ambassadors or other public ministers.

Second, and more importantly, the US Supreme Court also holds appellate jurisdiction; that is, it wields the power to review lower court rulings and to reverse, affirm, or modify those decisions. The vast majority of cases on the Supreme Court's docket get there as appeals of decisions made in inferior courts in the federal judiciary and in state supreme courts. These cases usually reach the Court by a losing party's request for a writ of certiorari, an order by the Supreme Court to the lower court to deliver all records of a particular case. Others reach the Court by certificate, a request placed by a lower court for help interpreting a law. Still, the Justices refuse to hear many of the thousands of cases delivered to the Court for review each year; most are denied because the Court agrees with the decision of the lower court or because the Justices do not feel the case is significant enough to merit its attention. At least four of the nine members of the Court must agree to hear a case, a practice referred to as "the rule of four." Because Justices tend to be extremely particular when it comes to adding more cases to the Court's docket, they select an average of only three hundred—less than 5% of all appeals requests—for review each year. The Supreme Court's annual term usually extends from October to July, or ten months. That means that if the Court accepts 300 cases, it must handle its cases at a rate of one per day, including weekends. (Now you see why the Justices are so finicky about those appeals.)

Once the Supreme Court agrees to accept a case, it schedules time to hear oral arguments from lawyers representing both sides. Following these presentations, the Justices recess to consider the oral arguments as well as court briefs, highly detailed documents filed by each side prior to appearances before the court. While in recess, the Chief Justice facilitates discussion, polls each Justice on his or her position in the case, and moderates debate until each member has settled on a decision. Considering that nearly every Supreme Court case is exceedingly controversial, it's quite staggering that some 30% of all the Court's decisions are unanimous. Most final rulings, however, are split; the majority opinion stands as the official edict of the Court, though dissenting Justices offer an explanation for their opposition to the final ruling. In addition to the majority and dissenting opinions, Justices may offer a concurring opinion that agrees with the majority but applies different reasoning for the decision.

The importance of the Court's rulings cannot be underestimated; its opinions clarify the scope of federal laws, establish precedents for lower courts, and, often, by deciding questions of public policy, can shape the social, economic, and political values of the nation.